1. Field of the Invention
This invention relates to feed arrangements for machine tools, and more particularly to feed apparatus for automatic lathes, of the type having a plurality of tubular stock-guiding spaces of different diameters, comprising an elongated cylindrical body defining the main axis of the apparatus and containing the aforementioned spaces, all of which have their longitudinal axes parallel to that of the main axis and equidistant from it.
2. Description of the Prior Art
Feed apparatus of this type is commercially available, e.g., from the assignee of this application, which markets such apparatus as model HYS or "Superhydrobar." FIGS. 1 and 2 of the accompanying drawings illustrate in a general manner this prior art apparatus in which a number of metal tubes, usually five such tubes of different diameters, are housed within an outer metal tube or jacket where they are held in place by a filler substance poured into the outer tube. The inner tubes constitute guides for bar stock to be machined.
The axes of the inner tubes of such apparatus should be strictly parallel to and equidistant from the main axis, which is that of the outer tube or jacket, if the apparatus is to perform properly. In the prior art design, these two requirements are substantially met by the expensive means of using tooling especially designed to hold the several tubes in place relative to one another while the liquified filler substance is poured in. In this complicated method, the ends of the tubes are secured in the proper relative positions, so that steps must also be taken to keep the tubes from bending in the middle, particularly in the case of the smallest tubes, during pouring and subsequent hardening of the filler. Although it would naturally be possible to prevent such bending by keeping the tubes vertical during the pouring operation, this approach presents other problems inasmuch as the tubes are usually some five meters long. If the tubes were positioned at an angle during pouring, there would be precisely the risk of their sagging.
Moreover, the requirement for concentricity, i.e, that the axes of the inner tubes should all be equidistant from that of the surrounding tube, is met only approximately in the prior art apparatus. In practice, it is necessary to insert small wedges or wedging cylinders at the location where the outer tube is held in place near the rear of the headstock of a lathe in order to ensure that whichever of the guide-tubes is in operation, i.e, the one brought into the bottom position by rotating the outer tube, is precisely aligned with the axis of the spindle of the lathe. It it were possible to ensure that the axes of all the inner tubes were situated exactly on a single circumference centered about the main axis of the apparatus, i.e., the axis of the outer tube, there would be no need for such wedging, which has to be carefully carried out depending upon the position of a certain inner tube within a certain outer tube. Briefly stated, the feed apparatus could be properly standardized, and its use could be simplified, if the requirement for axial concentricity could be strictly met.
This invention amounts to reversing the manner in which apparatus of the type in question was first constituted, viz., as a composite barrel or drum, somewhat resembling the cylinder of a revolver. Such composite apparatus differs from the present apparatus in that all the component tubes were of the same diameter, which simplified the construction and made it possible to achieve good accuracy without any great difficulty. The composite apparatus was made up by taking a number of tubes and joining them by means of hoops, braces, disks, etc., to form a sort of cage. This type of assembly was naturally also contemplated for producing apparatus of the type in question, especially the apparatus sold by the present assignee under the registered trademark "Hydrobar"; however, certain difficulties were encountered. Firstly, it was found very difficult to assemble tubes of different diameters to form a composite barrel or drum with sufficient accuracy of positioning because of the angular variations differing according to the diameters of the tubes and because of the difficulty of radial positioning, likewise considering the differences in tube diameter; and secondly, the great waste of space entailed by a composite barrel design and no longer tolerable as soon as large-diameter tubes were involved (adjacent to smaller-diameter tubes). The composite-barrel solution, i.e., the construction of a cage from its components, was therefore abandoned in favor of a design utilizing a filler material (as shown in FIG. 2, illustrating the prior art). In this design, however, the tubes were still the main elements of the structure, the filler substance being provided only to stabilize the locations of the tubes and to position them relative to one another in a fairly simple manner. Yet the tubes formed the main structure, the filler the supporting structure.